Vehicle transmissions typically have multiple gears. For a given speed of rotation of an input shaft of the transmission, each gear when engaged results in a different speed of rotation and/or direction of rotation of an output shaft of the transmission. The gears typically need to be engaged sequentially.
One example of a vehicle transmission has a park position, a reverse position, a neutral position, a high position, and low position. In the park position, the output shaft is locked and cannot rotate. In the reverse position, the output shaft rotates in a direction which results in the vehicle in which the transmission is provided to move in a reverse direction. In the high and low positions, the output shaft rotates in a direction which results in the vehicle in which the transmission is provided to move in a forward direction. In the low position, the output shaft rotates slower than in the high position, however more torque is applied in the low position than in the high position. The operator of the vehicle having the transmission selects the position of the transmission via a gear selector having positions corresponding to each of the positions of the transmission.
One typical shifting pattern, or sequence, in which the gears need to be engaged, of the type of transmission described above is sequentially: park, reverse, neutral, high, and low. Therefore, to get from the park position to the low position, the operator of the vehicle will have to engage the reverse, neutral, and high positions before finally engaging the low position. As would be understood, to get back to the park position from the low position, the positions have to be engaged in the reverse sequence.
In some applications, such as in utility vehicles, the operator of the vehicle often needs to switch between the low position and the reverse position. This would be the case for example when the vehicle is provided with a plow and is therefore being used to plow. As explained above, to change from one of the low and the reverse positions to the other of the low and the reverse positions, the operator needs to first engage the transmission into its neutral and high positions. Transmissions typically require that the gear (or gears) corresponding to the selected transmission position needs to be engaged before the following transmission position in the sequence can be selected. However, when the operator of the vehicle wants to select a position of the transmission, it is not uncommon that the gear (or gears) corresponding to this position are not properly aligned with the engagement mechanism being used to connect it to the output shaft, such as a shifting sleeve. This is sometimes referred to as a dog-on-dog condition. When this occurs, the operator is not capable of positioning the gear selector in the proper position until the gear is properly aligned with the shifting sleeve.
Furthermore, shifting sleeves typically have a set of teeth for engaging with a corresponding set of openings defined in the transmission gears for engaging the shifting sleeve to the transmission gears. To avoid premature wearing of both the teeth of the shifting sleeves and edges of the openings defined in the transmission gears, and to reduce noise from the relative movement of the shifting sleeves and transmission gears, the teeth are shaped to fit as tightly as possible in the openings. However, this requires that a shifting sleeve be almost perfectly aligned with a transmission gear for allowing engagement thereto, which may be difficult when the shifting sleeve and transmission gear rotate at significantly different speeds.
This increases the amount of time necessary to get from one gear position to the other and may cause rattling noise. It can also be somewhat upsetting to the operator to often have difficulty in engaging the gears, especially in the type of application described above where constant transmission position changes are necessary.
Therefore, there is a need for a vehicle transmission which facilitates the engagement of the gears of the transmission.